1. Field of the Invention
This invention relates to an antirotation structure for a combined oil ring for internal combustion engines.
2. Description of the Related Art
The internal cylindrical surface of the two-cycle engine cylinder has port openings. If a piston ring rotates in its circumferential direction and as a result the ring gap comes to the port opening position, the pair of end portions of the ring expand outward by its expanding force. If the ring moves up and down under that state, the end portions may be caught by the port opening edge.
In an engine with cylinder axis tilted to horizontal or almost horizontal position, if the ring rotates so that the ring gap comes to the lower position, lubricant oil may find its way through the gap into the combustion chamber while the engine is at rest. If the engine is started under that state, white smoke may be produced or consumption of lubricant oil may increase.
Since the above problems are caused by rotation of the ring in its circumferential direction, in some cases antirotation measures are taken for the ring.
Situations for employing the antirotation structure for the ring in various engines are as follows.
Diesel engines for construction equipment and marine applications with fewer number of starts and stops usually do not employ the antirotation structure for the ring.
Of the automobile gasoline engines frequently started and stopped, those with the cylinder axis tilted to horizontal or almost horizontal position usually employ the antirotation structure for the ring.
Conventionally, diesel engines with cylinder axis tilted to horizontal or almost horizontal position have been little employed in cars. Therefore those engines have not employed the antirotation structure for the ring. Recently, however, such diesel engines tend to be employed in cars.
Specific types of the antirotation structure for a compression ring employ generally,
1. Joint with internal notch.
2. Joint with side notch.
(Refer to JIS B 8032).
Antirotation structures for the 3-piece combined oil ring consisting of two side rails and a spacer expander are disclosed for instance in the following utility models.
1. Utility Model Laid-open No. Sho 56-165937
2. Utility Model Laid-open No. Hei 6-59660
3. Utility Model Publication No. Sho 56-9879
4. Utility Model Laid-open No. Hei 5-25064
5. Utility Model Laid-open No. Hei 3-32156.
An antirotation structure for the 2-piece combined oil ring consisting of an oil ring and a coil expander is disclosed in the following utility model.
1. Utility Model Laid-open No. Sho 57-31546.
Utility Model Laid-open No. Sho 56-165937 discloses an antirotation means in which the end portion of a side rail is bent in the axial direction and the bent portion is fit into a recess formed on the upper or lower surface of an oil ring groove to produce the antirotation effect. However, since the recess is formed on the upper or lower surface of an oil ring groove, a problem arises that the sealing effect between the side rail and the upper or lower surface of the oil ring groove lowers at the recess.
Utility Model Laid-open No.Hei 6-59660 discloses an antirotation means employing a dowel pin located in the radial direction on the upper or lower surface of an oil ring groove, with the pin partially exposed. However, this arrangement also has a problem, since the arcuate surface of the dowel pin is exposed from the upper or lower surface of the oil ring groove, the sealing effect between a side rail and the upper or lower surface of the oil ring groove becomes incomplete around the dowel pin. Another problem is that, since notches are formed on the internal surface in the end portions of the side rail, strength in that portion is poor in case of the reduced thickness in the radial direction of the side rail.
Utility Model Publication No. Sho 56-9879 and Utility Model Laid-open No.Hei 5-25064 describe antirotation means in which a spacer expander engages with a dowel pin, and the end portions of a side rail are bent in the axial direction so as to engage with the spacer expander. Utility Model Laid-open No. Hei 3-32156 describes antirotation means in which part of a spacer expander is bent inward so as to engage with a recess on the bottom surface of an oil ring groove, and the end portions of a side rail are bent in the axial direction so as to engage with the spacer expander. However, each of them has a problem that, when the side rail is treated by nitriding, the bending strength is reduced after the treatment and there is a possibility of breaking when it is bent.
Utility Model Laid-open No. Sho 57-31546 describes antirotation means in which portions of a coil wire at both ends of a coil expander are projected radially inwardly and outwardly, and the projected portions are respectively fit into the oil hole of an oil ring and into the oil drain hole of a piston. Incidentally, usually the outside circumferential surface of the coil expander is processed with centerless grinding in order to reduce pressure on the contact surface between the coil expander and the oil ring. However, the above structure makes the grinding process on the outside circumferential surface of the coil expander difficult because the portions of the coil wire at the ends of the coil expander are directed in the radial direction and projected from the outside circumferential surface of the coil expander. Another problem with the above structure is that since the end surfaces of the coil expander cannot be ground, stability at the joint end portion is poor. Still another problem with such a structure is that, since the overall length of the coil expander can not be changed after forming the coil expander, adjustment of expansion force cannot be made.